Combined frequency determining circuit and antenna



N 1m 3,6; 196m 6 J. A. KUEKEN 3,296,616

. COMBINED FREQUENCY DETERMINING CIRCUIT AND ANTENNA Filed June" 1, 1965 2 Sheets-sheet 1 Mln BY H

ATTORNEYS COMBINED FREQUENCY DETERMINING CIRCUIT AND ANTENNA Filed June 1 1965 J.` A. KUECKEN 2 Sheets-Sheet 2 FIG. 4

INVENTOR.

K CM uff/ K A. N H Tw AY B ATTORNEYS transistor. i form` of antenna for radiating the energy produced by the .oscillator and for` receiving the energy reflected from 3,296,616 `COMBINED FREQUENCY DETERMINING CIRCUI'I MAND` ANTENNA JohnwAauKuecken, Pittsford, N.Y., assignor to Avco Corporation,` Cincinnati, Ohio, a corporation of hio Filed June 1, 1965, Ser. No. 460,432

` Claims. (Cl. 343-8) p This;` invention `relates to circuits for `producing and radiating radio frequency energy and more particularly to =a`.cavty Hstructureused both as `the frequency deter- 1 mining element of an oscillator and as a slot type antn'iia for radiating the energy produced by the'o'scillator.

Proximity: fuze type devices normally utilize an oscilp lator operating in the VHF frequency `band and above.

the itargeti` used for` producing the doppler effect. Common forms of; antennas used are horn antennas, and slot antennas, with the` antenna being located separate and i remote frornthe oscillator tube or transistor.

` Priorart fuze devices of the typerdiscussed above have several disadvantages. First of all, since `the antenna is separate` from the oscillator, one impedance matching network is needed to couple the oscillator to a waveguide or coaxial; transmission line and another is needed to couple" ther line tothe antenna. The` use of one or two such networks is undesirable from several aspects. First, they produce a loss in the amplitude of the signal transmitted from the antenna and a lossrin the strength of the `signal coupled back to the oscillator to produce the doppler effect. Second, the use of thenetworks adds to the bulk and weight of the fuze as well as to its cost. All of these `factors `are desirably kept to a minimum.

Since, proximity fuzes are radar type devices intended to receive only their-own reflected signals, exact frequency control of the oscillator is not necessary except to the extent .needed to keep` the oscillator operating within the passiband ofl the antenna and the matching networks.

However, even this presents a problem in prior art fuzes since `the electrically small antennas generally used are very `high Q ldevices. Therefore the oscillator and antenna frequencies must be fairly accurately tracked in ordento keep the oscillator working within the pass band ofthe antenna and matching networks. This has neces sitated` .the use ;of frequency control arrangements in fuizeszof` the prior art with their attendant disadvantages of added Weight and cost.

Therpresentinvention is directed to a combined cavity and` :antenna structure which eliminates substantially all ofthe `disadvantages of the prior art fuze type devices discussedabove and which is also relatively simple in its construction and easy to fabricate. 1. The structure of the invention functions Iboth as the frequency determining circuit forthe oscillator as well as the antenna for radiating `energy produced by the oscillator and for receiving the reflected zenergy. In accordance with the invention, a cavity backed slot antenna is provided `as the frequency determining `circuit for the oscillator. The slot antenna formed in the cavity structure has an oscillator element, such as` a tube or transistor, coupled directly to it so that the.. energy produced by the oscillator is directly coupled to.` theuantenna for radiation. This eliminates both the coupling :networks and `the transmission line used where the; antenna is located separate from the oscillator. The structure also contains a feedback loop coupled to the `antenna by `which `both regenerative feedback and the States Patent 0 doppler feedback signal are coupled to the oscillator. In operation, the cavity structure determines the frequency at which the oscillator operates and since the oscillator element is connected directly to the cavity backed antenna the energy is coupled directly to the antenna for radiation into space. Reflected energy received by the antenna is coupled directly back to the oscillator to produce the doppler signal.

The cavity-antenna structure of the present invention may be readily constructed at relatively low cost and has significant electrical operating advantages over prior art devices of the same type. First of all, since the oscillator'element is mounted directl'y'to the structure, "there is no need for coupling and impedance matching networks. This eliminates the bulk and cost of such devices together with the signal losses they produce. Also, there is no problem with respect to tracking the frequency of the oscillator to the pass-band of either the matching networks or the antenna, since there are no such networks used in the invention and since the antenna is actually an integral part of the frequency determining circuit.

It is therefore an object of the present invention to provide an antenna for radiating the energy produced by an oscillator, the antenna also forming the frequency determining circuit of the oscillator.

Another object is to provide a cavity backed slot antenna structure which is also used as the frequency determining circuit of an oscillator, the slot antenna in the cavity also being used for radiating and receiving the energy produced by the oscillator.

An additional object is to provide a combined frequency determining cavity-antenna structure for an oscillator, with the oscillator being directly connected to the antenna without the use of matching and/or coupling networks.

Other objects and advantages of the present invention will become more apparent upon reference to the following specification and annexed drawings in which:

FIGURE 1 is a top plan view of the cavity-antenna structure;

FIGURE 2 is a side elevational view taken in section through lines 2--2 of FIGURE l;

FIGURE 3 is a schematic diagram showing an electrical circuit for the oscillator; and

FIGURE 4 is a perspective view, shown partially broken away, of another form of cavity.

Referring to FIGURES 1 and 2, the combined cavityantenna structure of the present invention is formed by a cup-shaped generally cylindrical piece 12 of conductive material having a top 1'3. T-he side wall of the piece 12 is shouldered down at 15 and a generally cylindrical disc 16 of conductive material is held in contact with piece 12 against shoulder 15 by any suitable conductive material, such as solder 17, placed therearound.

As can be seen, a cavity 18 is formed in the space between the top 13 of piece 12 and the disc member 16. Since the walls of the cavity are of conductive material, it can resonate electromagnetic energy therein at a frequency determined by its dimensions and in different modes dependent upon yboth the cavity dimensions and manner of excitation. The cavity 18 is in communication with a slot 20 cut diametrically across and through the top piece 13. A hole 22 is located at each end of the slo-t. The slot and holes form a slot antenna which is backed by cavity 18 with the holes 22 electrically loading the slot to form a so-called dumbbell type end-loaded slot antenna. The length and width of the slot as well as the diameter of the loading holes 22 are selected in accordance with the electrical characteristics required for the antenna. The slot is covered by a piece of tape 23, which illustratively may be fiber glass tape filled with an epoxy plastic com- 3. pound, thereby sealing the cavity 18 from moisture or other harmful constituents.

A pair of clips 24 of electrically conductive material are fastened, such as by spot welding 'or soldering, to the underside of the top piece 13 within the cavity, one on each side of the slot. The clips hold a transistor 28 mounted therebetween, this transistor serving as the oscillator element for the structure. The transistor has a pair of electrically conductive mounting studs 31 and 32, each stud being connected to one electrode of the transistor, for example the emitter and collector electrodes. It should be understood that a vacuum tube may also be utilized as the oscillator element but a semi-conductor is preferred since it may be more readily encapsulated and requires less in the way of power supplies.

The `structure also has a feedback loop 36r which is a piece of stiff wire having one end electrically connected to the top piece 13 yon one side of the slot. The other end of loop 36 is connected to one of the electrodes of the transistor, for example the base, and a portion of the loop lies parallel to the top piece 13 on the other side of the slot. Energy is coupled Ifrom the slot antenna to the loop 36 and therefore to the electrode of the transistor connected to the loop. The coupling coefficient can be adjusted by varying the position of the loop with respect to the sides of the slot and also by changing the length of the portion of the loop used for coupling.

A cable 37 is also provided. This cable runs along the top and side of they cavity walls and through the disc 16 into the lower portion of the cylinder 12. The cable has a number of wires (not shown) which :are connected to the electrodes of transistor 28 and to other circuit elements (not shown) for the oscillator and the oscillator pow-er supply (not shown) all of which are preferably located within the lower portion of cylinder 12 or at some other place remote from the cavity. The oscillator itself is of any suitable conventional configuration using a singleI resonant circuit, this resonant circuit being the cavity 18. The cable 37 may be taped or glued to the side Wall of piece 12.

Considering now the electrical operation of the structure, the transistor 28 has two of its electrodes connected directly to the top wall 13 of cavity 18 across the slot. For example, consider that the emitter electrode isconnected by stud 31 and a clip 24 to the top piece 13 on the same side of slot 20 to which the end of loop 36 is connected while the collector electrode is connected by stud 32 and the other clip 24 to the top .piece on the opposite side of the slot. Thus, the transistor 2.8 is connected emitter to collector directly across the slot so that energy produced by the transistor `is applied directly to the antenna for radiation thereby.

In the exemplary oscillator configuration being described regenerative feedback for the oscillator is provided by loop 36, one end of which is connected to top piece 13 on the side of the slot to which the emitter electrode is connected. Since the loop 36 has a portion which couples in-phase energy produced by the transistor from the slot antenna 20 back to the base, a regenerative feedback path is provided. Thus, the oscillator circuit is formed by transistor 28, the cavity 18 which acts `as a tuned resonant circuit connected between the collector and the emitter electrode of the transistor, and the feedback loop connected between the `slot and the base electrode of the transistor. Loop 36 also couples out-of-phase energy reflected back from the target and receive-d by the slot antenna back into the base of the transistor. This provides the doppler effect.

The lumped parameter equivalent for oscillator circuit produced by the cavity-antenna of FIGS. l and 2 is shown in FIGURE 3 wherein the tuned resonant circuit 46 shown by the lumped inductance an-d capacitance parameters corresponds to the equivalent parallel inductance and capacitan-ce produced by the cavity 18. The loop 36 is -illustrated by the tickler lcoil 47 which is coupled by slot 20 to the resonant circuit to feed the energy generated by the transistor in-phase back to the base of the transistor to produce oscillation and to couple alternatingly out-ofphase :and in-phase energy received from the target as the antenna moves relative to the target, to produce a doppler signal. The cable 37 has a number of wires which are connected to other elements and power supplies for the oscillator circuit. Any suitable conventional form of loscillator circuit may be used, many of which :are wellknown in the art. Therefore, the details of the various types of oscillators .are not described since the particular type of oscillator used is not important to the operation of the cavity-antenna of the present invention. For example, the base and collector electrodes may be connected across slot 20. By this arrangement an oscillator circuit is produced.

The antenna portion of the structure comprises both the cavity 18 and the slot 20` with its two holes 22 forming the end-loaded dumbbell slot antenna. Antennas of this general type are well-known in the art and the natural Q of an antenna of this type is suciently high to permit its use as t-he sole frequency determining element of the oscillator circuit.

It should be understood that the resonant frequency of the cavity 18, .and hence the frequency of operation of the oscillator 28, can be varied -by varying the physical l dimensions of the cavity, such as its shape, size, etc., and 'also by Varying the shape of the slot 20 and holes 22.

The cavity 18 is preferably excited in the TEM mode wherein the E vector lies generally transverse to the long dimension of the slot. Therefore, propagation through the slot will be in the sarne manner with the E vector Ibeing transverse thereto.

While the impe-dances of the oscillator circuits used may vary, a fairly wid-e range of impe-dances can be matched by positioning the transistor off-center of the slot. Minimum impedance is obtained at t-he end of the slot and maxim-um impedance at the center of the sl-ot. Additional impedance matching can be obtained by placing a capacitance across the slot.

FIGURE 4 shows another embodiment of the structure having better aerodynamic characteristics. Here, the top n piece 13 is crown-shaped to offer less wind resistance and the slot 20 and end-holes 22 can be more readily seen. The slot follows the contour of the crown. The cavity- 'antenna of this embodiment operates in the same manner as previously described.

As should Ibe apparent the cavity-antenna structure of the present invention has several advantages over other pri-or art structures of the same general type. First of all, the p-recision oscillator resonator cavities usually associated with such other prior art devices are eliminated and the simple readily constructed -cavity of the present invention is used instead. This cavity can 'be formed of two pieces, the cylinder 12 and disc 16, which may be stamped, die cast, drawn, or formed by any other suitable process. Additionally, two matching networks, one between the oscillator and the transmission line connecting the oscillator to the antenna, and another between the antenna and the line are eliminated as are the losses produced thereby. As another advantage, the frequency tracking problem between the cavity, matching networks and antenna is eliminated. Still further, the cavity-antenna structure serves as a good heat sink for the transistor oscillator.

While preferred embodiments of the invention have been described above, it will be understood that these are illustrative only, and the invention is limited solely by the appended claims.

What is claimed is:

1. A combined cavity-antenna structure comprising:

conductive means defining a cavity structure for propagating electromagnetic energy, said conductive means having a slot therein and together forming an antenna by which electromagnetic energy can be kradiated and received, and said cavity structure also having a resonant frequency,

andgoscillator means connected `directly to said conductive means, said cavity structure being the frequency determining element of an oscillator circuit including said oscillator means, and the antenna formed by the conductive means and slot radiating the `electromagnetic energy produced by the oscillator circuit.

2.11A1combined cavity-antenna structure comprising:

conductive means defining a cavity structure for propagating l electromagnetic energy, said conductive means having a slot therein and together forming an antenna by which electromagnetic energy can be radiated and received, `and said cavity structure also having a resonant frequency, oscillator means connected directly to said conductive means, said cavity: structure being the frequency determining element of an oscillator circuit including said `oscillator means,

and feedback means electrically coupled to the conductive .means and the oscillator means to provide a regenerative `signal for the oscillator means whereby said` oscillator means produces electromagnetic energywwhich is ;radiated by the antenna.

3. The combined cavity-antenna structure of claim 2 wherein the feedback means is connected to apply the out-of-phaseiand in-phase energy received by the, antenna after `reflection from a target to said oscillator means to produce thet doppler signal as the antenna moves rela- `tive to the f target.`

4. A combined cavity-antenna structure comprising:

a housing of conductive material forming a cavity structure for `propagating electromagnetic energy, said housing :having a slot therein and together forming an antenna by which electromagnetic energy can be radiatedtand received,

oscillator means `including a multi-element electron conductive devicehaving at least source, control and collector electrodes,

andmeans` fondirlectly connecting atleast two of said i electrodes to said housing at respective points thereon `on opposite `sides of the slot, the cavity structure forming a frequency determining circuit for said oscillator means and said antenna radiating the electromagnetic energy produced by the oscillator means.

SJThe `combined cavity-antenna structure of claim 4 whereinysaid housing is also formedwith a hole at each end ofthe slot `to end-load the antenna.

.i t `6. iA *combined cavity-antenna structure comprising:

a housing ,of conductive `material forming a cavity structure for` propagating electromagnetic energy,

saidhousing` having a slot therein andttogether forming an antenna `'by which electromagnetic energy can be -radiated and received,`

`oscillator means including a multi-element electron a frequency determining circuit for said oscillator means,

and feedback means electrically coupled to said housing and one of said electrodes for providing a regenerative signal feedback path between said frequency determining circuit and said electron conductive device whereby said oscillator means produces electromagnetic energy which is radiated by said antenna, the reflected in-phase and out-of-phase energy received by said antenna being coupled by said feedback means to said oscillator means to produce a doppler signal as the antenna moves relative to the target.

7. The combined cavity-antenna structure of claim 6 wherein said housing is also formed with a hole at each end of the slot to end-load the antenna.

8. A combined cavity-antenna structure comprising:

a housing of conductive material forming a cavity structure for propagating electromagnetic energy, said housing having a slot therein and together forming an antenna by which electromagnetic energy can be radiated and received,

oscillator means including a multi-element electron conductive device having at least source, control and collector electrodes,

means for directly connecting at least two of said electrodes to said housing at respective points thereon on opposite sides of the slot, the cavity structure forming a frequency determining circuit for said oscillator means,

and a feedback loop having one end thereof electrically connected to said housing on one side of said slot and the other end connected to one of said electrodes, said loop being positioned in said slot and electrically coupled to said housing for providing a regenerative feedback signal path between said frequency determining circuit and said electronic conductive device whereby said oscillator means produces electromagnetic energy which is radiated by said antenna.

9. The combined cavity-antenna structure of claim 8 wherein the feedback loop is so positioned with respect to the housing to couple in-phase and out-of-phase energy received by said antenna to said oscillator means, to produce a doppler signal as the antenna moves relative to a target, said antenna being coupled by said feedback loop to said oscillator means.

10. A combination cavity-antenna structure in accordance with claim 8 in which the means for connecting the electrodes to the housing comprises a pair of clips placed to match the antenna impedance with that of said conductive device.

References Cited by the Examiner UNITED STATES PATENTS 7/1954 Fales 343--767 7/ 1963 Wickersham 343-701 

6. A COMBINED CAVITY-ANTENNA STRUCTURE COMPRISING: A HOUSING OF CONDUCTIVE MATERIAL FORMING A CAVITY STRUCTURE FOR PROPAGATING ELECTROMAGNETIC ENERGY, SAID HOUSING HAVING A SLOT THEREIN AND TOGETHER FORMING AN ANTENNA BY WHICH ELECTROMAGNETIC ENERGY CAN BE RADIATED AND RECEIVED, OSCILLATOR MEANS INCLUDING A MULTI-ELEMENT ELECTRON CONDUCTIVE DEVICE HAVING AT LEAST SOURCE, CONTROL AND COLLECTOR ELECTRODES, MEANS FOR DIRECTLY CONNECTING AT LEAST TWO OF SAID ELECTRODES TO SAID HOUSING AT RESPECTIVE POINTS THEREON ON OPPOSITE SIDES OF THE SLOT, THE CAVITY STRUCTURE FORMING A FREQUENCY DETERMINING CIRCUIT FOR SAID OSCILLATOR MEANS, AND FEEDBACK MEANS ELECTRICALLY COUPLED TO SAID HOUSING AND ONE OF SAID ELECTRODES FOR PROVIDING A REGENERATIVE SIGNAL FEEDBACK PATH BETWEEN SAID FREQUENCY DETERMINING CIRCUIT AND SAID ELECTRON CONDUCTIVE DEVICE WHEREBY SAID OSCILLATOR MEANS PRODUCES ELECTROMAGNETIC ENERGY WHICH IS RADIATED BY SAID ANTENNA, THE REFLECTED IN-PHASE AND OUT-OF-PHASE ENERGY RECEIVED BY SAID ANTENNA BEING COUPLED BY SAID FEEDBACK MEANS TO SAID OSCILLATOR MEANS TO PRODUCE A DOPPLER SIGNAL AS THE ANTENNA MOVES RELATIVE TO THE TARGET. 